```
# import necessary libraries
import pandas as pd
# create your sample series
series = pd.Series([1, 3, 6, 10, 15, 21])
# define lambda function
calc_diff = lambda x, y: y - x
# find diff of diff using calc_diff and map()
difference = list(map(calc_diff, series[:-1], series[1:]))
diff_of_diffs = list(map(calc_diff, difference[:-1], difference[1:]))
# print results
print(diff_of_diffs)
```